3 Units of Chapter Hubble s Galaxy Classification 24.2 The Distribution of Galaxies in Space 24.3 Hubble s Law 24.4 Active Galactic Nuclei More Precisely 24-2 Relativistic Redshifts and Look-Back Time 24.5 The Central Engine of an Active Galaxy
4 24.1 Hubble s Galaxy Classification This pair of images shows the Coma cluster of galaxies. Almost every object visible is a galaxy.
5 24.1 Hubble s Galaxy Classification Spiral galaxies are classified according to the size of their central bulge.
6 24.1 Hubble s Galaxy Classification Type Sa has the largest central bulge, Type Sb is smaller, and Type Sc is the smallest. Type Sa tends to have the most tightly bound spiral arms with Types Sb and Sc progressively less tight, although the correlation is not perfect. The components of spiral galaxies are the same as in our own galaxy: disk, core, halo, bulge, and spiral arms.
7 24.1 Hubble s Galaxy Classification The Sombrero galaxy, with its large central bulge, is a type Sa. We cannot see the spiral arms, as they are edge-on.
8 24.1 Hubble s Galaxy Classification Similar to the spiral galaxies are the barred spirals.
9 24.1 Hubble s Galaxy Classification Elliptical galaxies have no spiral arms and no disk. They come in many sizes, from giant ellipticals of trillions of stars, down to dwarf ellipticals of less than a million stars. Ellipticals also contain very little, if any, cool gas and dust, and they show no evidence of ongoing star formation. Many do, however, have large clouds of hot gas, extending far beyond the visible boundaries of the galaxy.
10 24.1 Hubble s Galaxy Classification Ellipticals are classified according to their shape from E0 (almost spherical) to E7 (the most elongated).
11 24.1 Hubble s Galaxy Classification S0 (lenticular) and SB0 galaxies have a disk and bulge, but no spiral arms and no interstellar gas.
12 24.1 Hubble s Galaxy Classification The irregular galaxies have a wide variety of shapes. The small and large Magellanic Clouds are close neighbors to our own Milky Way.
13 24.1 Hubble s Galaxy Classification Here are several other irregular galaxies: AM and its neighbors on the left, and NGC 1569 on the right.
14 24.1 Hubble s Galaxy Classification A summary of galaxy properties by type
15 24.1 Hubble s Galaxy Classification Hubble s tuning fork is a convenient way to remember the galaxy classifications, although it has no deeper meaning.
16 24.2 The Distribution of Galaxies in Space Cepheid variables allow measurement of galaxies to about 25 Mpc away.
17 24.2 The Distribution of Galaxies in Space However, some galaxies have no Cepheids, and most are farther away than 25 Mpc. New distance measures are needed. Tully-Fisher relation correlates a galaxy s rotation speed (which can be measured using the Doppler effect) to its luminosity.
18 24.2 The Distribution of Galaxies in Space Type I supernovae all have about the same luminosity, as the process by which they happen doesn t allow for much variation. They can be used as standard candles objects whose absolute magnitude is known, and which can therefore be used to determine distance using their apparent magnitude.
19 24.2 The Distribution of Galaxies in Space With these additions, the cosmic distance ladder has been extended to about 1 Gpc
20 24.2 The Distribution of Galaxies in Space This is the Local Group of galaxies, about 45 galaxies within about 1 Mpc of the Milky Way
21 24.2 The Distribution of Galaxies in Space There are three spirals in this group the Milky Way, Andromeda, and M33. These and their satellites about 45 galaxies in all form the Local Group. Such a group of galaxies, held together by its own gravity, is called a galaxy cluster.
22 24.2 The Distribution of Galaxies in Space A nearby galaxy cluster is the Virgo Cluster; it is much larger than the Local Group, containing about 3500 galaxies.
23 24.2 The Distribution of Galaxies in Space This image shows the Abell 1689 cluster of galaxies, a very large cluster almost 1 billion parsecs away.
24 24.3 Hubble s Law Universal recession: all galaxies (with a couple of nearby exceptions) seem to be moving away from us, with the redshift of their motion correlated with their distance.
25 24.3 Hubble s Law These plots show the relation between distance and recessional velocity for the five galaxies in the previous figure, and then for a larger sample.
26 24.3 Hubble s Law The relationship (slope of the line) is characterized by Hubble s constant H 0 : recessional velocity = H 0 distance The currently accepted value for Hubble s constant is H 0 = 70 km/s/mpc Measuring distances using Hubble s law actually works better on farther away objects; random motions are overwhelmed by the recessional velocity.
27 24.3 Hubble s Law This puts the final step on our distance ladder
28 24.4 Active Galactic Nuclei About 20 25% of galaxies don t fit well into the Hubble scheme they are far too luminous. Such galaxies are called active galaxies. They differ from normal galaxies in both the luminosity and type of radiation they emit.
29 24.4 Active Galactic Nuclei The radiation from these galaxies is called nonstellar radiation. Many luminous galaxies are experiencing an outburst of star formation, probably due to interactions with a neighbor. These galaxies are called starburst galaxies, and we will discuss them later. The galaxies we will discuss now are those whose activity is due to events occurring in and around the galactic center.
30 24.4 Active Galactic Nuclei This active galaxy has star-formation rings surrounding a very luminous core.
31 24.4 Active Galactic Nuclei Active galaxies are classified into three types: Seyfert galaxies, radio galaxies, and quasars. Seyfert galaxies resemble normal spiral galaxies, but their cores are thousands of times more luminous.
32 24.4 Active Galactic Nuclei The rapid variations in the luminosity of Seyfert galaxies indicate that the core must be extremely compact
33 24.4 Active Galactic Nuclei Radio galaxies emit very strongly in the radio portion of the spectrum. They may have enormous lobes, invisible to optical telescopes, perpendicular to the plane of the galaxy.
34 24.4 Active Galactic Nuclei Radio galaxies may also be core dominated.
35 24.4 Active Galactic Nuclei Core-dominated and radio-lobe galaxies are probably the same phenomenon viewed from different angles.
36 24.4 Active Galactic Nuclei Many active galaxies have jets, and most show signs of interactions with other galaxies.
37 24.4 Active Galactic Nuclei Quasars quasi-stellar objects are starlike in appearance, but have very unusual spectral lines.
38 24.4 Active Galactic Nuclei Eventually it was realized that quasar spectra were normal, but enormously redshifted.
39 24.4 Active Galactic Nuclei Solving the spectral problem introduces a new problem quasars must be among the most luminous objects in the galaxy, to be visible over such enormous distances.
40 More Precisely 24-1: Relativistic Redshifts and Look-Back Time The redshift of a beam of light is its fractional increase in wavelength. Redshifts are measured directly; distances are calculated from them using Hubble s constant, which is uncertain. Astronomers therefore prefer to quote redshifts rather than distances. The look-back time is the time when light was emitted from a distant object; for very distant objects it is less than the redshift would indicate, as the object has receded in the meantime.
41 24.5 The Central Engine of an Active galactic nuclei have some or all of the following properties: high luminosity nonstellar energy emission Active Galaxy variable energy output, indicating small nucleus jets and other signs of explosive activity broad emission lines, indicating rapid rotation
42 24.5 The Central Engine of an Active Galaxy This is the leading theory for the energy source in an active galactic nucleus: a black hole, surrounded by an accretion disk. The strong magnetic field lines around the black hole channel particles into jets perpendicular to the magnetic axis.
43 24.5 The Central Engine of an Active Galaxy In an active galaxy, the central black hole may be billions of solar masses. The accretion disk is whole clouds of interstellar gas and dust; they may radiate away as much as 10 20% of their mass before disappearing.
44 24.5 The Central Engine of an Active Galaxy This pair of images shows evidence for a black hole at the center of NGC 4261.
45 24.5 The Central Engine of an Active Galaxy The central portion of M87 shows rapid motion and jets characteristic of material surrounding a black hole.
46 24.5 The Central Engine of an Active Galaxy One might expect the radiation to be mostly X and gamma-rays, but apparently it is often reprocessed in the dense clouds around the black hole and reemitted at longer wavelengths.
47 24.5 The Central Engine of an Active Galaxy Particles will emit synchrotron radiation as they spiral along the magnetic field lines; this radiation is decidedly nonstellar.
48 Summary of Chapter 24 Hubble classification organizes galaxies according to shape Galaxy types: spiral, barred spiral, elliptical, irregular Objects of relatively uniform luminosities are called standard candles ; examples include RR Lyrae stars and Type I supernovae The Milky Way lies within a small cluster of galaxies called the Local Group. Other galaxy clusters may contain thousands of galaxies
49 Summary of Chapter 24 (cont.) Hubble s Law: Galaxies recede from us faster the farther away they are Active galaxies are far more luminous than normal galaxies, and their radiation is nonstellar Seyfert galaxies, radio galaxies, and quasars all have very small cores; many emit high-speed jets Active galaxies are thought to contain supermassive black holes in their centers; infalling matter converts to energy, powering the galaxy
Chapter 24 Galaxies Units of Chapter 24 24.1 Hubble s Galaxy Classification 24.2 The Distribution of Galaxies in Space 24.3 Hubble s Law 24.4 XXActive Galactic Nuclei XXRelativistic Redshifts and Look-Back
Galaxies with Active Nuclei Active Galactic Nuclei Seyfert Galaxies Radio Galaxies Quasars Supermassive Black Holes Active Galactic Nuclei About 20 25% of galaxies do not fit well into Hubble categories
Galaxies, AGN and Quasars Physics 113 Goderya Chapter(s): 16 and 17 Learning Outcomes: Galaxies Star systems like our Milky Way Contain a few thousand to tens of billions of stars. Large variety of shapes
UNIT 4 - Galaxies XIV. The Milky Way galaxy - a huge collection of millions or billions of stars, gas, and dust, isolated in space and held together by its own gravity M110 M31 - Andromeda Galaxy A. Structure
Chapter 19 Galaxies Hubble Ultra Deep Field: Each dot is a galaxy of stars. More distant, further into the past halo disk bulge Barred Spiral Galaxy: Has a bar of stars across the bulge Spiral Galaxy 1
Lecture Outlines Chapter 23 Astronomy Today 8th Edition Chaisson/McMillan Chapter 23 The Milky Way Galaxy Units of Chapter 23 23.1 Our Parent Galaxy 23.2 Measuring the Milky Way Discovery 23-1 Early Computers
Galaxies Guiding Questions How did astronomers first discover other galaxies? How did astronomers first determine the distances to galaxies? Do all galaxies have spiral arms, like the Milky Way? How do
Lecture 19: Galaxies Astronomy 111 Galaxies What is a galaxy? Large assembly of stars, gas and dust, held together by gravity Sizes: Largest: ~1 Trillion stars (or more) Smallest: ~10 Million stars Milky
Galaxies & Introduction to Cosmology Other Galaxies: How many are there? Hubble Deep Field Project 100 hour exposures over 10 days Covered an area of the sky about 1/100 the size of the full moon Probably
7/7 The Nucleus of the MW its center 1. Can t see the nucleus in visible light too much stuff in the way. 2. Can observe radio waves from the nucleus see a strong radio source there Sagittarius A* or Sgr
15.1 Islands of stars Chapter 15 Galaxies and the Foundation of Modern Cosmology Cosmology: study of galaxies What are they 3 major types of galaxies? Spiral galaxies: like the milky way, look like flat,
Chapter 16 Homework Due: 11:59pm on Thursday, November 17, 2016 To understand how points are awarded, read the Grading Policy for this assignment. Question 1 Following are a number of distinguishing characteristics
Quasars and Active Galactic Nuclei (AGN) Astronomy Summer School in Mongolia National University of Mongolia, Ulaanbaatar July 21-26, 2008 Kaz Sekiguchi Hubble Classification M94-Sa M81-Sb M101-Sc M87-E0
Chapter 17 Active Galaxies and Supermassive Black Holes Guidepost In the last few chapters, you have explored our own and other galaxies, and you are ready to stretch your scientific imagination and study
Lecture 12: Galaxies View of the Galaxy from within The Milky Way galaxy Rotation curves and dark matter External galaxies and the Hubble classification scheme Plotting the sky brightness in galactic coordinates,
SOME NEGATIVE EFFECTS OF THE EXPANSION OF THE UNIVERSE. Lecture 22 Hubble s Law and the Large Scale Structure of the Universe PRS: According to modern ideas and observations, what can be said about the
ASTR 3830 Astrophysics 2 - Galactic and Extragalactic Phil Armitage office: JILA tower A909 email: firstname.lastname@example.org Spitzer Space telescope image of M81 Part two of a year-long introduction to astrophysics:
Chapter 23 The Milky Way Galaxy The Milky Way is our own galaxy viewed from the inside. It is a vast collection of more than 200 billion stars, planets, nebulae, clusters, dust and gas. Our own sun and
ASTR 1040: Stars & Galaxies Our wide world (universe) of Galaxies Expanding universe: Hubble s discovery #2 Challenge of measuring s in universe review methods used Subtle concept of Lookback time Active
Department of Physics and Geology Laboratory: Milky Way Astronomy 1402 Equipment Needed Quantity Equipment Needed Quantity Milky Way galaxy Model 1 Ruler 1 1.1 Our Milky Way Part 1: Background Milky Way
Galaxies Galaxies First spiral nebula found in 1845 by the Earl of Rosse. Speculated it was beyond our Galaxy. 1920 - "Great Debate" between Shapley and Curtis on whether spiral nebulae were galaxies beyond
Foundations Chapter of Astronomy 15 13e Our Milky Way Seeds Phys1403 Stars and Galaxies Instructor: Dr. Goderya Selected Topics in Chapter 15 A view our Milky Way? The Size of our Milky Way The Mass of
Galaxies Collection of stars, gas and dust bound together by their common gravitational pull. Galaxies range from 10,000 to 200,000 light-years in size. 1781 Charles Messier 1923 Edwin Hubble The distribution
Distances to galaxies Cepheids used by Hubble, 1924 to show that spiral nebulae like M31 were further from the Sun than any part of the Milky Way, therefore galaxies in their own right. Review of Cepheids
Quasars: Back to the Infant Universe Learning Objectives! What is a quasar? What spectral features tell us quasars are very redshifted (very distant)? What spectral features tell us they are composed of
Lecture 9 Quasars, Active Galaxies and AGN Quasars look like stars but have huge redshifts. object with a spectrum much like a dim star highly red-shifted enormous recessional velocity huge distance (Hubble
Lecture 27 Galaxy Types and the Distance Ladder December 3, 2018 1 2 Early Observations Some galaxies had been observed before 1900 s. Distances were not known. Some looked like faint spirals. Originally
Active Galaxies and Quasars Radio Astronomy Grote Reber, a radio engineer and ham radio enthusiast, built the first true radio telescope in 1936 in his backyard. By 1944 he had detected strong radio emissions
Chapter 30 Galaxies and the Universe Chapter 30: Galaxies and the Universe Chapter 30.1: Stars with varying light output allowed astronomers to map the Milky Way, which has a halo, spiral arm, and a massive
Other Galaxy Types Active Galaxies Active Galaxies Seyfert galaxies Radio galaxies Quasars Origin??? Different in appearance Produce huge amount of energy Similar mechanism a Galactic mass black hole at
C H A P T E R 15 THE MILKY WAY GALAXY 15-1 THE NATURE OF THE MILKY WAY GALAXY How do astronomers know we live in a galaxy? The hazy band of the Milky Way is our wheel-shaped galaxy seen from within, but
Active Galaxies and Galactic Structure Lecture 22 April 18th FINAL Wednesday 5/9/2018 6-8 pm 100 questions, with ~20-30% based on material covered since test 3. Do not miss the final! Extra Credit: Thursday
ROUND 2 - QUESTIONS 1. This question is about Hubble s law. The light received from many distant galaxies is red-shifted. (a) State the cause of this red-shift (1) expanding universe (b) State Hubble s
Lecture Outlines Chapter 25 Astronomy Today 7th Edition Chaisson/McMillan Chapter 25 Galaxies and Dark Matter Units of Chapter 25 25.1 Dark Matter in the Universe 25.2 Galaxy Collisions 25.3 Galaxy Formation
Chapter 20 Lecture The Cosmic Perspective Seventh Edition Galaxies and the Foundation of Modern Cosmology Galaxies and the Foundation of Modern Cosmology 20.1 Islands of Stars Our goals for learning: How
Active Galaxies & Quasars Normal Galaxy Active Galaxy Galactic Nuclei Bright Active Galaxy NGC 5548 Galaxy Nucleus: Exact center of a galaxy and its immediate surroundings. If a spiral galaxy, it is the
Goals: Galaxies To determine the types and distributions of galaxies? How do we measure the mass of galaxies and what comprises this mass? How do we measure distances to galaxies and what does this tell
ASTR 1120 General Astronomy: Stars & Galaxies!NNOUNCEMENTS HOMEWORK #6 DUE TODAY, by 5pm HOMEWORK #7 DUE Nov. 10, by 5pm Dark matter halo for galaxies Dark matter extends beyond visible part of the galaxy
29:50 Stars, Galaxies, and the Universe Final Exam December 13, 2010 Form A There are 40 questions. Read each question and all of the choices before choosing. Budget your time. No whining. Walk with Ursus!
AST-1002 Section 0459 Review for Final Exam Please do not forget about doing the evaluation! Bring pencil #2 with eraser No use of calculator or any electronic device during the exam We provide the scantrons
Astronomy A BEGINNER S GUIDE TO THE UNIVERSE EIGHTH EDITION CHAPTER 14 The Milky Way Galaxy Lecture Presentation 14.0 the Milky Way galaxy How do we know the Milky Way exists? We can see it even though
Lecture 30 History of the Galaxy Populations and Enrichment Galactic Evolution Spiral Arms Galactic Types Apr 5, 2006 Astro 100 Lecture 30 1 The Galactic Center The nature of the center of the Galaxy is
Chapter 17 Galaxies Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Galaxies Beyond the Milky Way are billions of other galaxies Some galaxies are spiral like
Galaxies Galaxies are collections of billons of stars; our home galaxy, the Milky Way, is a typical example. Stars, gas, and interstellar dust orbit the center of the galaxy due to the gravitational attraction
Lecture 14: Other Galaxies A2020 Prof. Tom Megeath Our Galaxy: Side View We see our galaxy edge-on Primary features: Disk: young and old stars where we live. Bulge: older stars Halo: oldest stars, globular
The Milky Way is just one of about 50 billion galaxies that are thought to exist. Just as stars can be classified using an H R diagram, galaxies can also be classified according to certain physical properties.
Chapter 25 (and end of 24): Lecture Notes In order to understand the Hubble Law and its implications both for estimating distances and for interpreting the evolution of the universe, you have to be comfortable
Normal Galaxies (Ch. 24) Here we will cover topics in Ch. 24 up to 24.4, but then skip 24.4, 24.5. The sections we are skipping are all about processes that occur in the centers of galaxies, so I d like
Reading Quiz Clickers The Cosmic Perspective Seventh Edition Our Galaxy 19.1 The Milky Way Revealed What does our galaxy look like? How do stars orbit in our galaxy? Where are globular clusters located
Guiding Questions Active Galaxies 1. Why are quasars unusual? How did astronomers discover that they are extraordinarily distant and luminous? 2. What evidence showed a link between quasars and galaxies?
The Galaxies The Milky Way Galaxy Is a spiral galaxy in which our solar system is located. The center of the galaxy lies in the Sagittarius Constellation. It is about 100,000 ly across, 2,000 ly thick,
Galaxies How did the universe form? 1 and 2 Galaxies Astronomers estimate that 40 billion galaxies exist in the observable universe The universe may contain over 100 billion galaxies Even a modest-sized
Chapter 15 The Milky Way Galaxy The Milky Way Almost everything we see in the night sky belongs to the Milky Way We see most of the Milky Way as a faint band of light across the sky From the outside, our
The Milky Way Galaxy (ch. 23) [Exceptions: We won t discuss sec. 23.7 (Galactic Center) much in class, but read it there will probably be a question or a few on it. In following lecture outline, numbers
Stars & Galaxies Chapter 27 Modern Earth Science Chapter 27, Section 1 27.1 Characteristics of Stars How do astronomers determine the composition and surface temperature of a star? Composition & Temperature
Astronomy 210 Final This Class (Lecture 40): The Big Bang Next Class: The end HW #11 Due next Weds. Final is May 10 th. Review session: May 6 th or May 9 th? Designed to be 2 hours long 1 st half is just
Exam 3 Astronomy 100, Section 3 Some Equations You Might Need modified Kepler s law: M = [a(au)]3 [p(yr)] (a is radius of the orbit, p is the rotation period. You 2 should also remember that the period
The Milky Way Milky Way : A band of and a The band of light we see is really 100 billion stars Milky Way probably looks like Andromeda. Milky Way Composite Photo Milky Way Before the 1920 s, astronomers
Astronomy 162, Week 8 Milky Way Galaxy, continued Patrick S. Osmer Spring, 2006 Rotation of Galaxy How do we know the galaxy is rotating, and how do we measure its rotation? Measure radial velocities of
ASTR 1040: Stars & Galaxies Prof. Juri Toomre TAs: Peri Johnson, Ryan Horton Lecture 23 Tues 10 Apr 2018 zeus.colorado.edu/astr1040-toomre Our wide world (universe) of Galaxies The rich range of galaxies:
Stars & Galaxies Chapter 27 Modern Earth Science Chapter 27, Section 1 27.1 Characteristics of Stars Composition & Temperature Scientists use the following tools to study stars Telescope Observation Spectral
2019 Astronomy Team Selection Test Acton-Boxborough Regional High School Written by Antonio Frigo Do not flip over this page until instructed. Instructions You will have 45 minutes to complete this exam.
ASTR 1040: Stars & Galaxies Super-bubble blowout in NGC 3709 Prof. Juri Toomre TAs: Ryan Horton, Loren Matilsky Lecture 22 Thur 8 Nov 2018 zeus.colorado.edu/astr1040-toomre Tour of Galaxies Look at complex
Chapter 14 The Milky Way Galaxy Spiral Galaxy M81 - similar to our Milky Way Galaxy Our Parent Galaxy A galaxy is a giant collection of stellar and interstellar matter held together by gravity Billions
Review of Chapters 14, 15, 16 Galaxies and the expansion of the Universe 5/4/2009 Habbal Astro 110-01 Review Lecture 36 1 Recap: Learning from Light How does light tell us what things are made of? Every
The Distance Ladder Learning Objectives! What is the distance ladder? How do we measure distances to objects in our Galaxy and to other galaxies?! How are the concepts of absolute magnitude and apparent
A100H Exploring the :, Dark Matter, Dark Energy Martin D. Weinberg UMass Astronomy email@example.com April 19, 2016 Read: Chaps 20, 21 04/19/16 slide 1 BH in Final Exam: Friday 29 Apr at
Beyond Our Solar System Chapter 24 PROPERTIES OF STARS Distance Measuring a star's distance can be very difficult Stellar parallax Used for measuring distance to a star Apparent shift in a star's position
Chapter 21 Galaxy Evolution How do we observe the life histories of galaxies? Deep observations show us very distant galaxies as they were much earlier in time (old light from young galaxies). 1 Observing
Chapter 15 The Milky Way Galaxy Guidepost This chapter plays three parts in our cosmic drama. First, it introduces the concept of a galaxy. Second, it discusses our home, the Milky Way Galaxy, a natural
Skills Worksheet Directed Reading A Section: The Life Cycle of Stars TYPES OF STARS (pp. 444 449) 1. Besides by mass, size, brightness, color, temperature, and composition, how are stars classified? a.
ASTR 1P02 Test 2, March 2017 Page 1 BROCK UNIVERSITY Test 2: March 2017 Number of pages: 9 Course: ASTR 1P02, Section 2 Number of students: 1193 Examination date: 4 March 2017 Time limit: 50 min Time of
Big Galaxies Are Rare! Potato Chip Rule: More small things than large things Big, bright spirals are easy to see, but least common Dwarf ellipticals & irregulars are most common Faint, hard to see Mostly
Black Holes in Hibernation Black Holes in Hibernation Only about 1 in 100 galaxies contains an active nucleus. This however does not mean that most galaxies do no have SMBHs since activity also requires
Astronomy C SSSS 2018 Galaxies and Stellar Evolution Written by Anna1234 School Team # Names 1 Instructions: 1. There are pictures of a number of galaxies in this test. However, as the DSO list for 2019
Active Galactic Nuclei How were they discovered? How common are they? How do we know they are giant black holes? What are their distinctive properties? Active Galactic Nuclei for most galaxies the luminosity
Homework #8 Due Wednesday, April 18, 11:59PM Covers Chapters 15 and 16 Estimated time to complete: 40 minutes Read chapters, review notes before starting This Week in Astronomy Credit: NASA/JPL-Caltech
Galaxies There are three basic types of galaxies: Spirals Ellipticals Irregulars To make a long story short, elliptical galaxies are galaxies that have used up all their gas forming stars, or they have
Some thoughts The Milky Way Galaxy How big is it? What does it look like? How did it end up this way? What is it made up of? Does it change 2 3 4 5 This is not a constant zoom The Milky Way Almost everything